When nodes in a private network become overloaded with intra-network calls, such calls will be re-routed from the private network to an available public network. The problem that arises when calls re-routed to hybrid and analogue public networks, is that call feature information available on ISDN and CCS7 private networks, such as calling and connected name, calling number and general feature related information, will no longer be available at the terminating node.
Arrangements whereby overflow calls on private networks and the like are switched over a public network have been described in U.S. Pat. No. 4,348,554 which issued to Richard L. Asmuth on Sept. 7, 1982. In the Asmuth patent, the foregoing problems are solved by describing a method of reducing the cost of providing private facilities, to simplify the procedure by which a customer may tailor its telephone services to assure cost minimization, and to further improve dedicated facility service. In particular, instead of purchasing a dedicated private network, a customer obtains virtual private network services over the public switched network, thereby minimizing its cost.
Information defining a virtual private network is stored in a data base, accessible by those telephone offices which have been defined as part of the virtual private network. This information includes a description of the capacity of the virtual network and resources. In response to a call received at one of the offices directed to the virtual network, a verification is made at the data base that the call is entitled to be completed via the virtual network and that an idle virtual resource on the public network remains for assignment to the call. The idle virtual resource is assigned to the call, and the call is completed over the public switched network. Although Asmuth provides an alternative service to virtual private customers, the problem associated with overflow calls remain for those customers who have existing dedicated private networks and services.
There is accordingly a requirement to provide a network service which will allow intra-network calls that overflow to the public network, and which has the ability to deliver private networking services that are transparent to the public network.